This application is a 371 of PCT/AU98/00267, filed Apr. 16, 1999.
The present invention relates to a novel, rapid and non-invasive method of monitoring the redistribution of water in protein-containing multi-phase systems during a mixing or processing step. The method of the invention is particularly applicable to food products. In a preferred embodiment, the invention relates to monitoring dough development and dough mixing properties using near infrared (NIR) spectroscopy, particularly through monitoring the variation in three specific absorbance wavelengths.
Dough mixing is the most critical stage in the production of bread products. The dough must be mixed to a stage loosely referred to as xe2x80x9coptimum developmentxe2x80x9d, and water must be added to the optimum absorption level of the flour for subsequent ease of processing and to ensure good end-product quality. The characteristics of the dough are partly affected by the type of flour used, for example xe2x80x9cvery strong flourxe2x80x9d, xe2x80x9cstrong flourxe2x80x9d, xe2x80x9cmedium flourxe2x80x9d or xe2x80x9cbiscuit flourxe2x80x9d. xe2x80x9cVery strongxe2x80x9d or xe2x80x9cstrongxe2x80x9d flours are characterised by their rheological xe2x80x9cstrengthxe2x80x9d properties as having a high degree of resistance to extension when a dough prepared from the flour is stretched using a standard testing device known as a Brabender Extensograph. They also have a long dough mixing or development time when mixed in either a commercial dough mixer or in one of the smaller test mixers, for example the Mixograph or the Farinograph. The dough also has a high degree of xe2x80x9cstabilityxe2x80x9d or resistance to break-down. Thus if mixed for a longer period than the optimum mixing time, such a dough will retain its characteristic mixing properties. Doughs which do not have strength breakdown, so that they have a sloppy, batter-like consistency, and can be mixed with little resistance. A dough which is prone to breakdown will cause enormous problems during processing. For example such a dough will not hold the gas produced by the yeast during baking, and thus will not rise so as to provide a good bread loaf volume and consistency. Conversely, a xe2x80x9cmediumxe2x80x9d strength flour will exhibit lower stability and have a higher degree of breakdown, while a xe2x80x9cbiscuitxe2x80x9d flour would be unsuitable for bread-making because of its poor stability. Stability is not required for biscuits. For these reasons, monitoring of dough development is of enormous importance to the baking industry.
A number of methods are commonly used to estimate dough development using laboratory scale mixers. The most popular measurement is that of mixing torque (Voisey, P. W., Miller, H. and Kloek, M., Cereal Chemistry, 1966 43 408-419; Voisey, P. W. Cereal Chemistry, 1974 51 841-847), using strain gauges attached to the mixer. An alternative method involves the measurement of the power consumption of the mixer (Anderson, R. A. and Lancaster, E. B. Cereal Chemistry, 1967 34 379-388; Kilborn, R. H. and Dempster, C. J. Cereal Chemistry, 1965 42 432-435). Alternatively, dough development in commercial mixers can be measured using a probe that, through a load cell, measures the force exerted by dough moving around the mixing bowl (Kilborn, R. H and Preston, K. R., Bakers Journal, 1981 16-19; Wilson, A. J. and Newberry, M. P., Food Technology in New Zealand, 1995 30 36-40). Each of these measurements, whilst useful, requires or is based on the results of direct physical interaction with the dough, and does not directly measure the chemical changes that occur during dough development. In addition, it has been reported that mixing beyond the time to peak resistance, as indicated by power consumption and mixograph produces higher quality loaves of bread (Zounis, S. and Quail, K. J., xe2x80x9cPredicting Test Bakery Requirements from Laboratory Mixing Testsxe2x80x9d, Journal of Cereal Science, 1997 25 185-196).
It is also well established that there is a relationship between glutenin content (or glutenin/gliadin ratio) and particular dough properties. See for example, Preston, K. R. and Tipples, K. H., Cereal Chemistry, 1980 57 314-320; MacRitchie, F., Journal of Cereal Science, 1985 3 221-230; and MacRitchie, F., Royal Society of Chemistry, London, 1986 132-146. During mixing, changes can occur in the composition of the polymeric phase of the gluten which relate to the dough rheological properties.
As used in this specification the term xe2x80x9cdoughxe2x80x9d refers to milled flour or wholemeal from a cereal, including but not limited to bread wheat (Triticum aestivum L.), added to water and other ingredients in any proportion which may include but are not limited to yeast, fat, salt and other Generally Recognized as Safe (GRAS) food ingredients, to which mechanical work is applied to develop a product useful for food application.
As used in this specification the term xe2x80x9cgliadin proteinxe2x80x9d is applied to a family of glutamine- and proline-rich proteins of wheat seed endosperm, which proteins are monomeric seed storage compounds and which subunits are encoded by genes on the short arms of homologous chromosomes 1 and 6 of wheat (Triticum aestivum, Triticum turgidum var. durum) and related cereal species. As used in this specification the term xe2x80x9cglutenin proteinxe2x80x9d is applied to a family of glutamine and proline-rich proteins of wheat seed endosperm, which proteins are a polymeric complex of disulfide-bonded seed storage polypeptide compounds and which subunits are encoded by genes on the long and short arms of homologous chromosomes 1 of wheat (Triticum aestivum, Triticum turgidum var. durum) and related cereal species.
The near infrared spectrum of flour consists of absorbances which are repeated at intervals across the wavelength range 800-2500 nm. The absorbances are due to specific chemical bonds and can be readily related to specific constituents of the flour.
NIR analysis has been used to monitor the principal constituents of flour, and to monitor water content of baked or processed foods through determination of specific absorbances in the near-infrared spectrum. It has been reported that NIR can be used to monitor the sucrose, fat, flour and water content of biscuit doughs (Osborne, B. G., Fearn, T., Miller, A. R. and Douglas, S., Journal of the Science of Food and Agriculture, 1984 35 99-105). NIR is most commonly used as a rapid analysis technique for quality control purposes, and usually involves calibration against a reference laboratory method. There are few studies on the use of NIR as a fundamental measurement tool, and even fewer on the use of NIR to follow chemical changes in materials. NIR has been used to follow the staling of bread (Wilson, R. H., Goodfellow, B. J., Belton, P. S., Osborne, B. G., Oliver, G. and Russell, P. L., J. Sci. Food. Agric. 1991 54 471-483) by fitting first order equations to spectral changes, and hence calculating rate constants for the staling process. On the basis of these results, the authors concluded that NIR could be used to gain information on the fundamental nature of the process that occurred during bread staling. However, the use of NIR to study the consistency of doughs has not been suggested.
Instruments and methods for determination of total protein content in dough or in whole grain have been described. U.S. Pat. No. 4,734,584 by Rosenthal discloses a NIR instrument for either reflectance or transmittance spectroscopy, depending on the sample chamber used, and with a range of wavelengths available for either mode. European Patent Application No. 511184 by Perten describes an instrument for very rapid NIR analysis of unground grain by reflectance spectroscopy, using a set of predetermined wavelengths in the range 1050-1400 nm provided by means of a continuous rotatable disc filter device. U.S. Pat. No. 5,258,825 by Reed and Psotka describes an apparatus for simultaneous visible and NIR analysis in a flour product, for determination of ash content and protein content respectively. The instrument may be used in either the reflectance or transmittance mode, and the preferred infrared wavelength is 1368 nm.
All of the instruments and methods described in the prior art are directed at measurement of protein content in wheat or other grains; protein content is loosely correlated with baking quality.
Not all of the wavelengths which are monitored in the near infrared reflectance spectrum (700-2500 nm) systematically vary in their intensities as a dough is processed. We have now found that the variation in absorbances at wavelengths in the second derivative spectrum (1160 nm (band of 1150-1170 nm)), 1200 (1190-1210 nm) and 1430 nm (band of 1420-1440 nm)) as the dough is mixed follows the same trend as mixer power consumption, and thus provides an estimate of dough development and breakdown.
The 1160 nm absorbance is the stretch-bend combination band of water, which is highly sensitive to the local environment of the water molecules, whilst the 1200 nm absorbance, which is a Cxe2x80x94H stretch second overtone, is thought to be due predominantly to protein. The 1430 nm absorbance is a mixture of two absorbances, due to water and protein. We have found that all three bands show a reduction in peak area as dough mixing progresses, reaching a minimum at optimum dough development, and an increase as the dough mixing continues past peak mixer power consumption. In the case of the 1160 nm water absorbance, this is thought to be due to the binding and subsequent release of water as dough development proceeds through optimum. Consistent results were obtained for unyeasted and full formula doughs made from four flours of different strengths using two different laboratory mixers.
These findings form the basis of a non-invasive and very rapid method of analysis of multi-phase protein-containing systems, especially dough, grain or grain products. For dough, the results are available as the dough is mixed. The method can be used to differentiate the flours on the basis of the difference in mixing time and stability, and shows the potential of the technique for providing information on the chemical processes that occur during dough development.
We have now also found that glutenin and gliadin differ in the second derivative spectrum: glutenin has an absorbance minimum at 2350 nm (band of 2346-2354 nm), whereas gliadin has an absorbance minimum at 2340 nm (2336-2344 nm), an absorbance minimum at 2310 nm (2300-2320 nm), and an absorbance maximum at 2195 nm (2190-2200 nm).
We have obtained clear evidence that the gliadin and glutenin fractions from flours of diverse genotypes consistently differ in specific spectral characteristics. Specific spectral differences have consistently been observed between gliadin and glutenin in isolates from five wheat varieties and a commercial flour, and consistent results have been obtained. These features (or their repeat absorbances) can be used to follow the changes that occur in the glutenin and gliadin content as dough is mixed.
In a first aspect, the invention provides a method of monitoring a processing step in a protein and water-containing multi-phase system, comprising the step of analysing said protein and water-containing system by near infrared spectroscopy. Preferably the multi-phase system is a food product.
In a further aspect, the present invention provides a method of monitoring dough development and breakdown during mixing and other processing, comprising the step of analysing the dough by near infrared (NIR) spectroscopy.
In a preferred embodiment there is provided a method for analysis of the time of development of optimal dough consistency for bread manufacture comprising the step of using near infrared reflectance spectrometry to measure absorbance at 1160 nm, 1200 nm and 1430 nm.
Preferably the following spectral differences of glutenin from gliadin in the second derivative spectrum are also analysed: an absorbance minimum for glutenin at 2350 nm (2346-2354 nm), whereas gliadin has an absorbance minimum at 2340 nm (2336-2344 nm); an absorbance minimum at 2310 nm (2300-2320 nm), and an absorbance maximum at 2195 nm (2190-2200 nm).
Preferably the NIR spectroscopic method utilises fast diode array detection, such that spectra can be recorded in under 10 seconds, more preferably under 1 second, thus providing improved monitoring of doughs as they are mixed.
Preferably the method monitors a plurality of specific absorbances that exhibit a change in peak area as dough mixing progresses, reaching a minimum or maximum at optimum dough development, and a change in the opposite direction as the dough mixing continues past peak mixer power consumption.
In another aspect, the invention provides a method for the monitoring of glutenin and gliadin in a dough or other product derived from grain, comprising the step of using NIR spectroscopy to measure spectral differences of glutenin and gliadin in the second derivative spectrum, namely for glutenin an absorbance minimum at 2350 nm (2346-2354 nm) and for gliadin an absorbance minimum at 2340 nm (2336-2344 nm), an absorbance minimum at 2310 nm (2300-2320 nm) and an absorbance maximum at 2195 nm (2190-2200 nm) or the overtones thereof.
Optionally other stretch and or bend fundamental, combination or overtone bands of water and/or other fundamental, combination or overtone bands due to the Cxe2x80x94H bonds in protein or lipid are also measured.
In a third aspect of the invention there is provided a method for predicting the change in glutenin and gliadin content in grain, wholemeal, flour, and dough, or is another product derived from said grain as described above.
It will be clearly understood that while the invention is described in detail for bakery products, particularly bread, the invention is equally applicable to other food and non-food multi-phase systems that involve the redistribution of water during a mixing or similar processing step. The person skilled in the art will readily be able to adapt the methods described herein for dough to other systems, using routine trial and error experimentation.
According to a fourth aspect, the invention provides an apparatus for NIR spectroscopic analysis of a grain, wholemeal, flour, dough, or is another product derived from said grain, comprising:
a) a source of near-infrared radiation;
b) a means for detection said near-infrared radiation; and
c) means whereby the dough or other product is exposed to said rear-infrared radiation source in appropriate relation to the detection means,
wherein either the source or detector is specific for the desired near-infrared radiation wavelength.
For analysis of dough according to the invention either the source or the detector is specific for wavelengths of 1160, 1200 and 1430 nm.
For determining relative proportions of glutenin and gliadin in a dough, the wavelengths will be those of the absorbance maxima and minima in the second derivative spectrum, as defined above, ie. 2530 nm, 2340 nm, 2310 nm and 2195 nm or their repeats.
The means c) for exposure of the sample to be analyzed to the source will depend on the nature of the sample, and the person skilled in the art will readily appreciate suitable devices. For example, a spectrometer may be positioned over a dough mixing vessel such that the dough surface is at the focal point of the source and detector.
Two principal types of detector are suitable for use in the apparatus of the invention. Most advantageously a diode array detector is used, since this enables a very large number of wavelengths to be measured virtually simultaneously, thus enabling the rapid measurement desirable in monitoring a fast process such as dough mixing. Alternatively a simple fixed filter device using transmission filters suitable for the desired wavelengths, and one or more additional filters to correct the spectra for the effects of scatter may be used. Diode array detectors are more expensive than filter instruments, although with improved technology the cost is becoming cheaper all the time. Fixed filter devices are slower but cheaper; they may be more suitable for certain applications.
In a number of the different aspects of the invention either reflectance NIR spectroscopy or transmittance NIR spectroscopy may be used. For transmittance spectroscopy a transmission probe is necessary, and suitable on-line probes are available for use in process monitoring applications. Reflectance spectroscopy is preferred for analysis of dough, as this is completely non-invasive and can be performed using a reflectance or interactance probe, or using the instrumentation alone. The person skilled in the art will readily be able to test which mode is most suitable for a given purpose.
The method of the present invention can be directly applied to equipment for the monitoring of optimal dough processing, and for the objective prediction of dough properties through NIR analysis of grain, wholemeal, flour or wheat products.
While the invention is described in detail in relation to wheat flour doughs, it will be clearly understood that the invention is also applicable to any cereal, grain or grain product derived from any grain in which glutenin and gliadin are present, including but not limited to mixed-grain doughs comprising rye, oats, barley and/or maize.